1. Field of the Invention
The present invention relates to an image display device and method for improving an image darkness recognition performance. More particularly, the present invention relates to an image display device having a Liquid Crystal Display (LCD) for improving an image darkness recognition performance, in which a reference brightness value of an image is detected by analyzing a process of human color recognition and a process of human color response such that a dark region of the image can be correctly recognized, and method for improving an image darkness recognition performance thereof. A brightness of the image is adjusted such that a specific region is not excessively bright or dark, and the user can recognize the image.
2. Background of the Prior Art
Portable wireless terminals, such as a mobile communication terminal and a Personal Digital Assistant (PDA), have become popular. Using the portable wireless terminals, the users can make a telephone call and manage their schedules. In addition, the users can take a picture with a built-in camera module and watch satellite broadcasting. Thus, the features of the portable wireless terminals have become popular.
Portable wireless terminals with displays have a problem concerning image quality. Features of still picture images taken by a digital camera may be adjustable based on the environment. Thus, a recognition performance for the darkness of the image does not matter. However, when a moving picture is displayed or the user watches real-time broadcasting, it is often difficult to correctly recognize a specific image due to a small-sized display of the portable wireless terminal. For example, it is difficult to correctly recognize some images, such as an image taken against the light, an image of a dark object taken at a dark place, and an image taken of an object that is lighter than its surroundings but still dark.
Most of the recent portable wireless terminals use liquid crystal displays (LCDs) as displays. Liquid crystal is an intermediary substance between a liquid state and a solid state depending on temperature. Liquid crystal generally is in a solid state at a temperature lower than 40-50 degrees below zero. Therefore, the LCD cannot be used as a display at that temperature. When a voltage is applied to the LCD at room temperature, the liquid crystal changes from a disordered liquid state to a liquid-solid state.
FIG. 1 is a perspective diagram illustrating a physical structure of a conventional Twist Nematic (TN) LCD.
Referring to FIG. 1, the TN LCD comprises polarizing filters, alignment layers, and a liquid crystal layer. The polarizing filters are arranged along the perpendicular polarizing axes and the light twists 90 degrees as it passes through the liquid crystals. In the TN LCD, the liquid crystals are controlled by the voltage. When the voltage is applied, the liquid crystal molecules are rearranged vertically. When the voltage is removed, the liquid crystal molecules have no order. In such a state of disorder, the TN LCD cannot operate as a display. In order to solve the above problem, a continuous property of the liquid crystal, such as the arrangement of the liquid crystal molecules is affected by neighboring molecules, is utilized. If one end of the liquid crystal is anchored, all liquid crystal molecules are not erected when the voltage is applied, but smoothly inclined from a lower side to an upper side with respect to the anchored axis. Meanwhile, when the voltage is removed, the erected liquid crystal molecules are inclined in a direction of the anchored axis because of the continuous property.
However, where the continuous property is used, a perfect black region cannot be obtained due to the inherent physical structure of the LCD. Also, some of the light may be transmitted. That means that the LCD structure easily expresses a bright region but has difficulty expressing a dark region.
Human visual recognition for a low brightness image is greater for a large-sized monitor, for example, a TV monitor than a small-sized LCD mounted on a portable wireless terminal. In addition, when an image has both a bright region and a dark region, human visual adaptation for the recognition performance for the dark region is high. However, for the LCD of the portable wireless terminal which is small-sized, human eye tends to be adapted to the brightness of the image displayed on the LCD. Due to this tendency, a dark image cannot be correctly detected when a bright region and a dark region coexist.
That is, the image display device having the LCD has a limitation in expressing the darkness of the image due to the physical structure of the LCD. Also, users tend to adjust to the brightness of the small image and therefore, a dark image cannot be correctly detected. That is, since human visual adjustment for the dark region of the small image for the LCD is low, it is difficult to detect the displayed image